Hydraulic elevator safety device



April 25, 1961 c. BRANDON HYDRAULIC ELEVATOR SAFETY DEVICE Filed Aug. 22, 1958 jzwerz 0% 6 ZjfQrfdOm United States HYDRAULIS ELEVATOR SAFETY DEVICE Carl Brandon, Detroit, Mich., assignor to Montgomery Elevator Company,

This invention relates to a safety device for hydraulic elevators, and in particular it relates to a construction of the hydraulic cylinder and ram which prevents overtravel of the ram at the upper end of the cylinder.

Hydraulic elevators are normally extremely safe in operation, but it is possible for malfunction of the driving mechanism to cause the elevator to crash into the overhead structure. The likelihood of serious damage or injury to persons or freight in the elevator is increased by reason of the greater operating speeds of modern hydraulic elevators.

The present invention provides a very simple mechanism for exerting a back pressure on the ram as it approaches the limit of its upward travel so as to stop the ram even though the hydraulic mechanism is continuing to supply liquid under pressure to the cylinder.

The present invention utilizes a tapered safety ring in the upper end of the cylinder, and an outwardly extending cushion ring on the lower end of the ram, the maximum diameter of the cushion ring being slightly less than the minimum diameter of the safety ring. As the ram appreaches the limit of its travel the cushion ring moves into the tapered safety ring, and an increasing back pres sure is exerted upon the cushion ring. By proper dimensioning of the cushion ring this back pressure may be built up to the point where there is a restraining force in excess of the lifting force on the ram. A small outlet bore lets the hydraulic liquid out of the space above the cushioning ring, and a bleed pipe returns it to the hydraulic system outside the cylinder.

The invention is illustrated in a preferred embodiment in the accompanying drawing, which is a fragmentary, vertical sectional view of the upper end of a hydraulic cylinder with the hydraulic ram shown in solid lines at the upper limit of its travel, and in broken lines at a lower position, a portion of the ram being in section to show the width of the cushion ring.

Referring to the drawing in greater detail, a hydraulic cylinder has an internally extending safety ring 6 supported at its upper end by means of a mounting flange 7. A circumferential flange 8 at the upper end of cylinder 5 provides a mounting for an annular cylinder head 9 through which a ram 10 extends. Surrounding the ram 10 within cylinder head 9 is packing 11 which is compressed against a bushing 12 by means of a packing gland 13. Bushing 12 is divided into a base portion 12a and a pressure relief ring 12b through which 'a fine pressure relief bore 14- communicates with a passage 15 through cylinder head 9 from which a bleed tube 16 may return liquid to an inlet pipe 17 through which liquid under pressure may be supplied to cylinder 5 for reciprocating ram 10. Bore 14 is of substantially smaller diameter than inlet pipe 17.

Safety ring 6 has an upper portion 18 which is parallel with the surface of ram 16, and a lower portion 19 which tapers from its lower end 20 to its upper end 21 so that, eifectively, the upper end of cylinder 5 is tapered.

At the lower end of ram 10 is an outwardly extending cushion ring 22 the maximum diameter of which is slightatent 1y less than the minimum diameter of safety ring 6. The upper surface 23 of cushion ring 22 is in a plane transverse to the axis of ram 10.

As seen in the drawing, cushion ring 22 moves into the tapered portion 19 of safety ring 6 as ram 10 approaches the upper limit of its travel, so as to constantly decrease the clearance between the cushion ring and safety ring. This exerts an increasing back pressure on the cushion ring; and to prevent excessive pressures from developing above the cushion ring and forcing liquid past the packing 11, the liquid above the ring may escape through the extremely narrow space between ram 10 and bushing 12a, passing out of the cylinder through outlet bore 14, passage 15, and returning to the liquid supply pipe 17 through the bleed pipe 16. The space between ram 19 and bushing 12a is exaggerated-in practice it is the minimum practical space which may be provided.

Let it be assumed for the sake of illustration that the bottom of ram 10 is 6 inches in diameter, and that cushion ring 22 is 7 inches in diameter. The total area of the ram and the ring is 38.465 square inches; and if liquid is supplied through pipe 17 at a pressure of 300 pounds per square inch, there is a maximum lift of 11,539.50 pounds on the ram.

Cushion ring 22 is /2 inch wide-i.e., it projects /2 inch radially from the surface of ram 10. Its outside radius being 3.5 inches and its inside radius 3 inches, it has an area of 10.2 square inches. A back pressure on this size cushion ring 22 of 1132 p.s.i. will overcome the entire lifting force; and such a back pressure is pos-' sible by the time the cushion ring reaches the position seen in the drawing. A slight reduction in rain diameter, thus increasing the area of the ring, permits a reduction in the back pressure per square inch while keeping the same total restraining force. Thus, overtravel of the ram may be absolutely prevented by the construction illustrated in the drawing.

It is obvious that overtravel of the ram as the elevator moves down could be prevented in the same Way by providing another safety ring 6 which would be mounted in an inverted position in the bottom of cylinder 5. This structure, and its operation, are described in more detail and claimed in application 834,886, filed August 19, 1959, a continuation-in-part'of this application.

The foregoing detailed description is given for clearness of understanding only and no unnecessary limitations are to be understood therefrom, as modifications will be obvious to those skilled in the art.

I claim:

1. In a hydraulic elevator system: a cylinder; a ram upper end of the cylinder, said bushing being provided with a fine outlet bore of substantially smaller diameter than the inlet pipe, and the clearance between said bushing and the ram being extremely small; packing above the bushing in sealing contact with the ram; bleed means connecting said outlet bore with the hydraulic means outside the cylinder; an an outwardly extending cushion ring which is positioned on the ram to move into the area surrounded by the safety ring as the ram approaches the top limit of its travel, the maximum diameter of the cushion ring being slightly less than the minimum diameter of the safety ring, and one of said rings having a surface which is so tapered that the clearance between the rings decreases as the cushion ring moves within the safety ring, whereby an increasing back pressure is exerted on the cushion ring to prevent overtravel of the ram at the top of the cylinder, and liquid between the cushion ring and the safety ring is forced out of the cylinder through the outlet bore in the bushing to prevent liquid from being forced past the packing.

2. In a hydraulic elevator system: a cylinder; a ram reciprocable in said cylinder; hydraulic means including an inlet pipe supplying liquid under pressure for reciprocating said ram; an annular cylinder head having packing means embracing the ram; a bushing in the cylinder head beneath the packing means, the clearance between said bushing and the ram means being extremely small, and said bushing and cylinder head being provided with a fine outlet bore of substantially smaller diameter than the inlet pipe; a bleed pipe connecting said bore with the hydraulic means outside the cylinder; a safety ring mounted in the cylinder just below the bushing, the lower portion of said safety ring defining a space which tapers toward its upper end, and the upper portion of said ring being substantially parallel to the surface of the ram; and an outwardly extending cushion ring on the lower end of the ram, the maximum diameter of the cushion ring being slightly less than the minimum diameter of the safety ring, said cushion ring having an upper surface substantially perpendicular to the ram and being positioned to move into the tapered space to decrease the clearance between the rings as the ram approaches the upper limit of its travel, whereby an increasing back pressure is exerted on the cushion ring to prevent overtravel of the ram, and liquid abovethe cushion ring is forced out of the cylinder through said outlet bore to prevent liquid from being forced past the packing means.

3. In a hydraulic elevator system: a cylinder; a ram reciprocable in said cylinder, there being substantial clearance between the surface of the ram and the upright.

cylinder Wall; guide and packing means at the top of the cylinder closely embracing the ram and effectively sealing the upper end of said cylinder; means supplying liquid under pressure to said cylinder for reciprocating said ram; an inwardly extending safety ring mounted in the upper end of the cylinder; and an outwardly extending cushion ring which is positioned on the ram to move into the area surrounded by the safety ring as the ram approaches the top limit of its travel, the maxim-um diameter of the cushion ring being slightly less than the minimum diameter of the safety ring, and one only of said rings having a surface which is so tapered that the clearance between the rings decreases as the cushion ring moves within the safety ring, whereby an increasing back pressure is exerted on the cushion ring to prevent overtravel of the ram at the top of the cylinder.

4. In a hydraulic elevator system: a cylinder; a ram reciprocable in said cylinder, there being substantial clearance between the surface of the ram and the upright cylinder wall; guide and packing means at the top of the cylinderclosely embracing the ram andefiectively sealing the upper end of said cylinder; hydraulic means supplying liquid under pressure to said cylinder for reciproeating said ram; an inwardly extending safety ring mounted in the upper end of the cylinder, said ring having a portion which defines a tapered space; and an outwardly extending cushion ring on the lower end of the ram, the maximum diameter of the cushion ring being slightly less than the minimum diameter of the safety ring, said cushion ring being positioned to move into the tapered space to decrease the clearance between the rings as the ram approaches the top limit of its travel, whereby an increasing back pressure is exerted on the cushion ring to prevent overtravel of the ram at the top of the cylinder.

5. In a hydraulic elevator system: a cylinder; a ram reciprocable in said cylinder, there being substantial clearance between the surface of the ram and the upright cylinder wall; guide and paclL'ng means at the top of the cylinder closely embracing the ram and effectively sealing the upper end of said cylinder; hydraulic means supplying liquid under pressure to said cylinder for reciprocating said ram; an inwardly extending safety ring mounted within the upper end of the cylinder, said safety ring defining a space which tapers toward its upper end; and an outwardly extending cushion ring on the lower end of the ram, the maximum diameter of the cushion ring being slightly less than the minimum diameter of the safety ring, said cushion ring having an upper surface substantially perpendicular to the ram and being positioned to i move into the tapered space to decrease the clearance between the rings as the ram approaches the upper limit of its travel, whereby an increasing back pressure is exerted on the cushion ring to prevent overtravel of the ram.

6. In a hydraulic elevator system: a cylinder which has a tapered upper end portion; a ram reciprocable in said cylinder, said ram having a circumferentially enlarged lowerend portion the maximum diameter of which is substantially less than the inside diameter of the cylinder but only slightly less than the minimum diameter of the tapered upper end portion of the cylinder; guide and packing means atthe top of the cylinder closely embracing the ram and effectively sealing the upper end of the cylinder; and hydraulic means supplying liquid under pressure tothe cylinder for reciprocating said ram, the enlarged end portion of the ram moving into the tapered end portion of the cylinder to decreasethe clearance between the ram and the cylinder wall as the ram approaches the top limit of its travel, whereby an increasing back.

pressure is exerted on the enlarged portion of the ram to prevent overtravel of the ram at the top of the cylinder.

References Cited in the file of this patent UNITED STATES PATENTS 1,495,949 Carroll May 27, 1924 1,759,516 Miller et a1. May 20, 1930 1,829,451 McNab Oct. 27, 1931 1,876,023 Rosenberry Q. Sept. 6, 1932 1,876,024 Rosenberry Sept. 6, 1932 2,198,196 Goldup Apr. 23, 1940 2,493,602 Sterrett Jan. 3, 1950 2,655,002 Terhune Oct. 13, 1953 2,882,869 Krap-f Apr. 21, 1959 2,884,903 Pauly May 5,1959 

